The present invention relates generally to systems for controlling the operation of an internal combustion engine, and more specifically to systems for compensating for atmospheric humidity effects on the operation of an internal combustion engine.
Differing levels of specific humidity in the atmosphere are known to impact the operation of internal combustion engines generally, and of spark-ignited engines in particular. For example, in spark-ignited, natural gas engines, increased levels of specific humidity tend to slow combustion by decreasing heat release rates and also by increasing the duration of individual combustion events.
Heretofore, systems have been devised to compensate for such adverse humidity effects by manipulating three main engine operating parameters; namely lambda (xcex), which is generally a function of air-to-fuel ratio, ignition timing and, in cases where the engine includes a turbocharger, boost pressure. One such system is described in U.S. Pat. No. 5,735,245 to Kubesh et al. which discloses a control system for determining specific humidity as a function of relative humidity and intake air temperature, and modifying fuel flow, spark timing and boost pressure commands as a function of the computed specific humidity.
However, the Kubesh et al. system has a number of drawbacks associated therewith. For example, in addition to specific humidity the modified fuel flow command is also a function of the oxygen content of the engine exhaust gas, and the Kubesh et al. system thus requires a universal exhaust gas oxygen (UEGO) sensor for operation thereof. This unnecessarily adds system cost and raises reliability concerns as well. As another example, the modified spark timing command in the Kubesh et al. system is a function only of the specific humidity value and a default spark timing command. Since spark timing is known to vary as a function of other engine operating conditions, the Kubesh et al. spark timing modification technique is capable of accurately modifying spark timing only in a narrow range of such engine operating conditions.
What is therefore needed is a humidity compensation system that overcomes the foregoing drawbacks and provides a low-cost, highly accurate humidity compensation strategy.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a humidity compensation system for an internal combustion engine comprises means for determining a specific humidity of air entering an intake manifold of an internal combustion engine, a fuel system responsive to a fueling command to supply fuel to the engine and a control circuit determining an adjusted air-to-fuel ratio command as a function of the specific humidity and a default air-to-fuel ratio command, the control circuit producing the fueling command as a function of the adjusted air-to-fuel ratio command.
In accordance with another aspect of the present invention, a method of compensating for atmospheric humidity effects on the operation of an internal combustion engine comprises determining a specific humidity of air entering an intake manifold of an internal combustion engine, computing an adjusted air-to-fuel ratio command as a function of the specific humidity and a default air-to-fuel ratio command, and fueling the engine based on the adjusted air-to-fuel ratio command.
In accordance with a further aspect of the present invention, a humidity compensation system for an internal combustion engine comprises means for determining a specific humidity of air entering an intake manifold of an internal combustion engine, an engine speed sensor producing an engine speed signal indicative of a rotational speed of the engine, an ignition system responsive to a timing signal to ignite an air-fuel mixture within the engine, and a control circuit determining an adjusted ignition timing command as a function of the specific humidity, the engine speed signal and a default ignition timing command, the control circuit producing the timing signal as a function of the adjusted ignition timing command.
In accordance with still a further aspect of the present invention, a method of compensating for atmospheric humidity effects on the operation of an internal combustion engine comprises determining a specific humidity of air entering an intake manifold of an internal combustion engine, determining a rotational speed of the engine, computing an adjusted ignition timing command as a function of the specific humidity, the rotational speed of the engine and a default ignition timing command, and controlling ignition timing of the engine based on the adjusted ignition timing command.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.